# Copyright 2025 Google LLC.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

name: Check PR Up-to-Date

on:
  pull_request:
    types: [opened, synchronize]

permissions:
  contents: read
  pull-requests: write

jobs:
  check-up-to-date:
    runs-on: ubuntu-latest
    # Skip for bot PRs
    if: ${{ !contains(github.actor, '[bot]') }}
    concurrency:
      group: check-pr-${{ github.event.pull_request.number }}
      cancel-in-progress: true
    steps:
      - name: Checkout repository
        uses: actions/checkout@v6
        with:
          fetch-depth: 2  # Sufficient for rev-list comparison

      - name: Check if PR is up-to-date with main
        id: check
        run: |
          # Fetch the latest main branch
          git fetch origin main

          # Check how many commits behind main
          BEHIND=$(git rev-list --count HEAD..origin/main)

          echo "commits_behind=$BEHIND" >> $GITHUB_OUTPUT

          if [ "$BEHIND" -gt 0 ]; then
            echo "::warning::PR is $BEHIND commits behind main"
            exit 0  # Don't fail the check, just warn
          else
            echo "PR is up-to-date with main"
          fi

      - name: Comment if PR needs update
        if: ${{ steps.check.outputs.commits_behind != '0' }}
        uses: actions/github-script@v9
        with:
          script: |
            const behind = ${{ steps.check.outputs.commits_behind }};
            const COMMENT_COOLDOWN_HOURS = 24;
            const COOLDOWN_MS = COMMENT_COOLDOWN_HOURS * 60 * 60 * 1000;

            // Check for recent similar comments
            const { data: comments } = await github.rest.issues.listComments({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: context.payload.pull_request.number,
              per_page: 10
            });

            const hasRecentComment = comments.some(c =>
              c.body?.includes('commits behind `main`') &&
              c.user?.login === 'github-actions[bot]' &&
              new Date(c.created_at) > new Date(Date.now() - COOLDOWN_MS)
            );

            if (!hasRecentComment) {
              await github.rest.issues.createComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: context.payload.pull_request.number,
                body: `📊 **PR Status**: ${behind} commits behind \`main\`\n\nConsider updating your branch for the most accurate CI results:\n\n**Option 1**: Use GitHub's "Update branch" button (if available)\n\n**Option 2**: Update locally:\n\`\`\`bash\ngit fetch origin main\ngit merge origin/main\ngit push\n\`\`\`\n\n*Note: If you use a different remote name (e.g., upstream), adjust the commands accordingly.*\n\nThis ensures your changes are tested against the latest code.`
              });
            }